Ionomer composition for golf ball, production method thereof and golf ball using the same

ABSTRACT

The present invention provides a golf ball with excellent abrasion-resistance, durability and resilience having an ionomer resin cover therein. The ionomer composition for the golf ball of the invention comprises a reaction product obtained by reacting a telechelic copolymer having functional groups introduced in both terminals of a binary copolymer formed by copolymerizing an olefin monomer having 2 to 8 carbon atoms and an unsaturated carboxylic acid having 2 to 18 carbon atoms, and/or a ternary copolymer formed by copolymerizing an olefin monomer having 2 to 8 carbon atoms, an unsaturated carboxylic acid having 2 to 18 carbon atoms and an unsaturated carboxylic acid ester with a hydroxyl group-containing compound or an isocyanate group-containing compound, wherein at least 10 mole % of a carboxylic group in said reaction product is neutralized with an inorganic metal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel ionomer composition for a golfball, which can be preferably used for producing the golf ball, aproduction method thereof, and a golf ball using the composition.

2. Description of the Related Art

A wound-core golf ball having a balata cover, a two-piece or three-piecegolf ball having an ionomer cover, and the like are known as aconventional golf ball. A wound-core golf ball having a balata cover hasgood shot feeling and controllability, but is expensive due to thecomplicate production steps, and also has problems such as poordurability and abrasion-resistance. A golf ball having an ionomer coveris excellent in resilience, abrasion-resistance and molding ability dueto the relative hardness thereof, but has problems such as poor shotfeeling and controllability.

Therefore, the improvements of the shot feeling and the controllabilityof the ionomer cover have been proposed, for example, in JapaneseUnexamined Patent Publication Nos. H01-308577, H05-277208, H07-132152,H08-182777, H11-500776, and 2001-515529. For example, JapaneseUnexamined Patent Publication No. H01-308577 discloses a technique ofblending a hard ionomer and a soft ionomer. Japanese Unexamined PatentPublication No. H05-277208 discloses a technique of using 2 or morekinds of ionomer resins having a relatively low modulus. JapaneseUnexamined Patent Publication No. H07-132152 discloses that a heatedmixture of an ionomer resin, a terpolymer consisting of α-olefin, anunsaturated carboxylate and an unsaturated carboxylic acid, and aglycidyl group-containing α-olefin copolymer resin is used as a baseresin of the cover. Japanese Unexamined Patent Publication No.H08-182777 discloses that a heated mixture of three kinds comprising anionomer resin, a maleic anhydride-modified olefin copolymer and aglycidyl group-modified styrene-based block copolymer having JIS-Ahardness of from 30-90 is used as a base resin of the cover. JapaneseUnexamined Patent Publication No. H11-500776 discloses a productionmethod of a composition for the golf ball cover, comprising saponify apolymer with an inorganic metal base to produce a polymer salt withsaponification degree of about 1 to 50%, wherein the polymer comprises afirst monomer component containing an olefin monomer having 2 to 8carbon atoms, a second monomer component containing an acrylate esterhaving 4 to 22 carbon atoms based on an unsaturated carboxylic acid, andan optional third monomer component containing at least one monomerselected from the group consisting of carbon monoxide, sulfur dioxide,an unsaturated monocarboxylic acid, an olefin having 2 to 8 carbon atomsand a vinyl ester or a vinyl ether of an alkyl acid having 4 to 21carbon atoms. Japanese Unexamined Patent Publication No. 2001-515529discloses an acid copolymer such as ethylene-methacrylic acid or acomposition including an ionomer and an adipic acid component.

SUMMARY OF THE INVENTION

According to the improving techniques described above, although the shotfeeling of the ionomer covers is somewhat improved, theabrasion-resistance and the resilience tend to be lowered. Thus, thereis a desire for achieving a golf ball having a higher level of theresilience, the abrasion-resistance and the shot feeling which are wellbalanced.

The present invention has been achieved in view of the above problemsand provides an ionomer composition for a golf ball, comprising areaction product obtained by reacting a telechelic copolymer havingfunctional groups introduced in both terminals of a binary copolymerformed by copolymerizing an olefin monomer having 2 to 8 carbon atomsand an unsaturated carboxylic acid having 2 to 18 carbon atoms, and/or aternary copolymer formed by copolymerizing an olefin monomer having 2 to8 carbon atoms, an unsaturated carboxylic acid having 2 to 18 carbonatoms and an unsaturated carboxylic acid ester with a hydroxylgroup-containing compound or an isocyanate group-containing compound,wherein at least 10 mole % of a carboxylic group in said reactionproduct is neutralized with an inorganic metal.

Also, the present invention provides a production method of an ionomercomposition for a golf ball, comprising the steps of:

obtaining a reaction product by reacting a telechelic copolymer havingfunctional groups introduced in both terminals of a binary copolymerformed by copolymerizing an olefin monomer having 2 to 8 carbon atomsand an unsaturated carboxylic acid having 2 to 18 carbon atoms, and/or aternary copolymer formed by copolymerizing an olefin monomer having 2 to8 carbon atoms, an unsaturated carboxylic acid having 2 to 18 carbonatoms and an unsaturated carboxylic acid ester with a hydroxylgroup-containing compound or an isocyanate group-containing compound;and

neutralizing the carboxylic group of said telechelic copolymer or theresultant reaction product with an inorganic metal compound.

Namely, a gist of the present invention resides in the use of thereaction product obtained by reacting the telechelic copolymer havingfunctional groups introduced in both the terminals thereof with ahydroxyl group-containing compound or an isocyanate group-containingcompound, wherein at least 10 mole % of a carboxylic group in saidreaction product is neutralized with an inorganic metal as an ionomerused for the golf ball. Use of the above reaction products improvesresilient performance and abrasion-resistance while being soft.

According to the present invention, a golf ball well balanced inresilience, abrasion-resistance and good shot feeling can be obtained.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(1) An Ionomer Composition for the Golf Ball of the Present Invention

The ionomer composition for the golf ball of the present inventioncomprises a reaction product obtained by reacting a telechelic copolymerhaving a functional group introduced in both terminals of a binarycopolymer formed by copolymerizing an olefin monomer having 2 to 8carbon atoms and an unsaturated carboxylic acid having 2 to 18 carbonatoms, and/or a ternary copolymer formed by copolymerizing an olefinmonomer having 2 to 8 carbon atoms, an unsaturated carboxylic acidhaving 2 to 18 carbon atoms and an unsaturated carboxylic acid esterwith a hydroxyl group-containing compound or an isocyanategroup-containing compound, wherein at least 10% or more of a carboxylicgroup in said reaction product is neutralized with an inorganic metal.

First, the telechelic copolymer having a functional group introduced inboth terminals of the binary copolymer formed by copolymerizing anolefin monomer having 2 to 8 carbon atoms and an unsaturated carboxylicacid having 2 to 18 carbon atoms, and/or a ternary copolymer formed bycopolymerizing an olefin monomer having 2 to 8 carbon atoms, anunsaturated carboxylic acid having 2 to 18 carbon atoms and anunsaturated carboxylic acid ester will be explained.

The above olefin monomer having 2 to 8 carbon atoms is an aliphaticunsaturated hydrocarbon having one double bond in a molecule, includingfor example, ethylene, propylene, butene, pentene, hexene, heptene andoctene. Among them, ethylene and propylene are preferable, and ethyleneis more preferable. The olefin monomers can be used alone or as amixture of two or more of them.

The above unsaturated carboxylic acid having 2 to 18 carbon atoms is acompound having 2 to 18 carbon atoms and containing at least oneethylenically unsaturated double bond and a carboxylic group in amolecule, more preferably an α,β-unsaturated carboxylic acid having 3 to8 carbon atoms. Examples of the unsaturated carboxylic acid having 2 to18 carbon atoms include acrylic acid, methacrylic acid, fumaric acid,maleic acid, crotonic acid (trans-2-butenoic acid), isocrotonic acid(cis-2-butenoic acid), sorbic acid, citraconic acid and mesaconic acid;in particular, acrylic acid and methacrylic acid are preferable.

Examples of the above unsaturated carboxylic acid ester include amethyl, an ethyl, a propyl, a n-butyl or an isobutyl ester of acrylicacid, methacrylic acid, fumaric acid, maleic acid, crotonic acid(trans-2-butenoic acid), isocrotonic acid (cis-2-butenoic acid), sorbicacid, citraconic acid and mesaconic acid; in particular, the ester ofthe acrylic acid or a methacrylic acid is preferable.

As the above binary copolymer, particularly preferred is a binarycopolymer obtained by copolymerizing ethylene and (meth)acrylic acid,and as the ternary copolymer, particularly preferred is a ternarycopolymer obtained by copolymerizing ethylene, (meth)acrylic acid and(meth)acrylic acid ester.

The content of the olefin monomer in the above binary and ternarycopolymer is 1% by mass or more, more preferably 5% by mass or more,further preferably 10% by mass or more, further more preferably 50% bymass or more, and 99% by mass or less, preferably 95% by mass or less,further preferably 80% by mass or less. When the content of the olefinmonomer is outside of the above range, the resilience of the resultantionomer composition may become insufficient.

The ternary copolymer preferably contains the unsaturated carboxylicacid in an amount of 1 mass % or more, more preferably 5 mass % or more,even more preferably 8 mass % or more, and preferably contains theunsaturated monomer having the acid functional group in an amount of 50mass % or less, more preferably 40 mass % or less, even more preferably30 mass % or less. If the content of the unsaturated carboxylic acid isoutside the above range, the impact resilience of the obtained ionomercomposition may become insufficient.

The present invention uses the telechelic copolymer having a functionalgroup introduced in both terminals of the binary copolymer and/or theternary copolymer. Herein, “both terminals” mean the both terminals of amain chain of the telechelic copolymer, and the functional groupsintroduced in both terminals are not derived from the unsaturatedcarboxylic acid, but are ones introduced into both terminals of thecopolymer by an another method that will be described later.

Examples of the functional groups introduced in terminals include acarboxyl group, a hydroxyl group, an amino group, an isocyanate group,halogen, a nitro group, a thiol group and an epoxy group. Preferable isa hydroxyl group, an amino group or an isocyanate group. Also,functional groups in both terminals of the binary copolymer and ternarycopolymer may be different or the same, but preferably is the same.

As the production method of the telechelic copolymer used in the presentinvention, a well known method can be employed. For example, thetelechelic copolymer can be synthesized using a radical initiator as apolymerization catalyst under the conditions of reaction pressure ofabout 100 to 300 KPa and reaction temperature from 150° C. to 350° C. ina tank reactor equipped with a stirring machine in the same manner as inthe production of a high pressure polyethylene. When an initiator or achain transfer agent capable of introducing a functional group is used,a functional group can be introduced in both terminals of the copolymerobtained.

Examples of an initiator capable of introducing a hydroxyl group includehydrogen peroxide,2,2′-azobis{2-[1-(2-hydroxyethyl)-2-imidazoline-2-yl]propane}dihydrochloride(VA-60 available from Wako Pure Chemical Industries, Ltd.),2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide](VA-086 availablefrom Wako Pure Chemical Industries, Ltd.), and2,2′-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide} (VA-080 available from WakoPure Chemical Industries, Ltd.); examples of an initiator capable ofintroducing a carboxyl group include2,2′-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate (VA-057available from Wako Pure Chemical Industries, Ltd.); examples of aninitiator capable of introducing an amino group include2,2′-azobis(2-methylpropionamidine)dihydrochloride (V-50 available fromWako Pure Chemical Industries, Ltd.). Also, using an initiator capableof introducing an allyl group, 2,2′-azobis[N-(2-propenyl)-2-methylpropionamide] (VF-096 available from Wako PureChemical Industries, Ltd.), it may be modified into a desired functionalgroup such as an epoxy group by introducing an allyl group followed byconducting an addition reaction or an oxidation reaction. Further, analkoxyamine type initiator having various functional groups can belisted.

As a chain transfer agent capable of introducing a functional groupinclude, examples of the chain transfer agent capable of introducinghalogen, include carbon tetrachloride and carbon tetrabromide.Preferably, once halogen is introduced, and then halogen is replacedwith a nitro group, a thiol group, an amino group, a hydroxyl group orthe like. Examples of a chain transfer agent capable of introducing ahydroxyl group include mercaptoethanol. Also, a functional group X canbe introduced in the terminals by using an addition splitting type chaintransfer agent having a structure of CH₂═C(CH₂X)Y, where X═Br or SO₂Ar.When the same functional group is introduced into both terminals of thebinary copolymer and/or the ternary copolymer, it is preferable to adoptone capable of introducing the same functional group as the initiatorand the chain transfer agent.

Also, a method of introducing an isocyanate group at the terminals mayinclude, for example, a method wherein a hydroxyl group or an aminogroup is once introduced at the terminals of the copolymer followed bybeing reacted with a polyisocyanate, or a method wherein an amino groupis once introduced followed by being reacted with phosgene to bemodified into an isocyanate group.

The polyisocyanate may include, for example, an aromatic polyisocyanatesuch as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, a mixture of2,4-toluene diisocyanate and 2,6-toluene diisocyanate (TDI),4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate(NDI), 3,3′-bitolylene-4,4′-diisocyanate (TODI), xylylene diisocyanate(XDI), tetramethylxylylene diisocyanate (TMXDI), paraphenylenediisocyanate (PPDI); and an alicyclic polyisocyanate or an aliphaticpolyisocyanate such as 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI),hydrogenated xylene diisocyanate (H₆XDI), hexamethylene diisocyanate(HDI), isophorone diisocyanate (IPDI) and norbornene diisocyanate(NBDI). The above polyisocyanate may be used alone or as a mixture oftwo or more thereof.

The hydroxyl group-containing compound used in the present invention isnot particularly limited as long as it has a hydroxyl group. Examples ofthe hydroxyl group-containing compound are a monool containing onehydroxyl group and a polyol containing at least two hydroxyl groups.

The above monool may include, for example, an aliphatic alcohol having 1to 20 carbon atoms such as methanol, ethanol, n-propanol, isopropanol,butanol, pentanol, hexanol, dodecyl alcohol and stearyl alcohol; phenolor a derivative thereof such as phenol, o-cresol, m-cresol, p-cresol(hereinafter, ortho, meta and para isomers are sometimes simply denotedas o-, m-, and p-, respectively), dimetylphenol, o, m, p-ethylphenol, o,m, p-n-propylphenol, o, m, p-isopropylphenol, o, m, p-phenylphenol, o,m, p-benzylphenol and cumylphenol; and an aralkyl alcohol having 7 to 20carbon atoms such as benzyl alcohol and phenethyl alcohol.

Examples of the above polyol include an aliphatic polyol, an aromaticpolyol and a polymer polyol.

Examples of the above aliphatic polyol include an aliphatic diol such asethylene glycol, 1,3-propanediol, 1,2-propanediol, 1,3-butanediol,2-methyl-propanediol, 1,4-butanediol, neopentyl glycol, pentamethyleneglycol, hexamethylene glycol, octamethylene glycol, decamethyleneglycol, dodecamethylene glycol, 1,4-cyclohexane dimethanol, diethyleneglycol, dipropylene glycol, triethylene glycol, tetraethylene glycol andpentaethylene glycol; and an aliphatic triol such as glycerin,trimethylolpropane and hexanetriol.

Examples of the above aromatic polyol include biphenyl or a derivativethereof such as 2,2′-dihydroxybiphenyl and 4,4′-dihydroxybiphenyl; abis(hydroxyaryl)alkane (alkane having 1 to 6 carbon atoms) such asbis(hydroxyphenyl)methane, bis (hydroxyphenyl)ethane andbis(hydroxyphenyl)propane; a bis (alkyl-substituted hydroxyphenyl)alkanesuch as bis (3-methyl-4-hydroxyphenyl)methane, bis(3-methyl-4-hydroxyphenyl)ethane, bis(3,5-dimethyl-4-hydroxyphenyl)methane and bis(3,5-dimethyl-4-hydroxyphenyl)ethane; a bis(hydroxyaryl)cycloalkane(cycloalkane having 3 to 12 carbon atoms) such asbis(hydroxyphenyl)cyclohexane; a bis(hydroxyaryl)carboxylic acid(carboxylic acid having 2 to 6 carbon atoms) such asbis-4,4′-(hydroxyphenyl)butanoic acid; a terpenediphenol such as1,4-di(alkyl-substituted hydroxyphenyl)-p-methane; and alsodi(hydroxyphenyl)ether, di(hydroxypheny)thioether,di(hydroxypheny)ketone, and di (hydroxypheny)sulfoxide.

Examples of the above polymer polyol include a polyether polyol such aspolyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG) andpolyoxytetramethylene glycol (PTMG); a condensed polyester polyol suchas polyethylene adipate (PEA), polybutylene adipate (PBA) andpolyhexamethylene adipate (PHMA); a lactone polyester polyol such aspoly-ε-caprolactone (PCL); a polycarbonate polyol such aspolyhexamethylene carbonate; an acryl polyol; and a polybutadienepolyol. These may be used as a mixture of at least two or more of them.Among them, a polyol having a molecular weight of 200 to 10000 ispreferable, and polyoxytetramethylene glycol (PTMG) and polybutadienepolyol are more preferable.

Also, the present invention may use an isocyanate group-containingcompound as well as a hydroxyl group-containing compound, instead ofreacting only the hydroxyl group-containing compound with the telecheliccopolymer. This is because the hydroxyl group-containing compounddescribed above can be easily changed to the isocyanate group-containingcompound by reacting with a polyisocyanate. Namely, the reason is thatif such an isocyanate group-containing compound is used, the embodimentof reacting the isocyanate groups of the isocyanate groups bothterminated the telechelic copolymer with hydroxyl groups of the hydroxylgroup-containing compound can be easily changed to the embodiment ofreacting hydroxyl groups of the hydroxyl groups both terminatedtelechelic copolymer with an isocyanate group-containing compound.

The ionomer composition of the present invention is a reaction productobtained by reacting the telechelic copolymer with the hydroxylgroup-containing compound or the isocyanate group-containing compound,and preferably, at least 10 mole % of said reaction product isneutralized with an inorganic metal. The degree of neutralization of thecarboxylic group in said reaction product is preferably 10 mole % ormore, more preferably 20 mole % or more, and even more preferably 30mole % or more. When the degree of neutralization of the carboxylicgroup is less than 10 mole %, an ionomerization effect becomes small,resulting in insufficient abrasion-resistance and resilience. On theother hand, because of saturation of the ionomerization effect, thedegree of neutralization of the carboxylic group is preferably 95 mole %or less, more preferably 90 mole % or less, and even more preferably 80mole % or less. Additionally, the degree of neutralization of thecarboxylic group is a molar ratio of mole number of neutralizedcarboxylic groups relative to the total mole number of carboxylic groupscontained in said reaction product.

The degree of the neutralization is calculated from the amount of thematerials fed. It can also be calculated, for example, by the followingformula, using the mole number of a unneutralized carboxyl group([COOH]) of the unsaturated carboxylic acid in the reaction productdetermined by thermally fusing the reaction product into tetrahydrofuranand titrating with potassium hydroxide having a normal concentration,and the mole number of the neutralized carboxyl group ([COOM])calculated by metal analysis.Degree of the neutralization(mole %)=[COOM]/([COOH]+[COOM])×100

A metal analysis, for example, a monovalent metal such as sodium may becarried out using, for example, 180-80 Type Polarized Zeeman AtomicAbsorption Spectrophotometer manufactured by Hitachi, Ltd., and ananalysis of a bivalent metal such as zinc may be carried out using, forexample, Sequential Type ICP Optical Emission Spectrometer SPS 1100manufactured by Seiko Instruments Inc.

The above inorganic metal for neutralizing the carboxyl group may be ametal selected from the group consisting of the 1st group to the 17thgroup, lanthanoids and actinoids of the periodic table.

The preferable inorganic metal can include an alkali metal such assodium, potassium and lithium; a divalent metal such as magnesium,calcium, zinc, barium and cadmium; a trivalent metal such as aluminumand neodymium; and other metals like tin and zirconium, more preferableare sodium, lithium, zinc and magnesium. The inorganic metals can beused alone, or in a combination of two or more thereof.

The slab hardness of the ionomer composition for the golf ball ispreferably 20 or more, more preferably 30 or more, even more preferably40 or more, and preferably 70 or less, more preferably 65 or less, evenmore preferably 60 or less in shore D hardness. If the ionomercomposition has the slab hardness of less than 20, the ionomercomposition may be too soft for the cover, and resulting in the loweredabrasion-resistance and resilience. On the other hand, if the ionomercomposition has the slab hardness of more than 70 in shore D hardness,the ionomer composition is too hard, and may result in the crack of thecover, due to the impact of hitting the golf ball with the club.

Next, a production method of the ionomer composition for the golf ballof the present invention will be explained.

The production method of the ionomer composition for the golf ball ofthe present invention comprises steps of obtaining a reaction product byreacting a telechelic copolymer having functional groups introduced inboth terminals of a binary copolymer formed by copolymerizing an olefinmonomer having 2 to 8 carbon atoms and an unsaturated carboxylic acidhaving 2 to 18 carbon atoms, and/or a ternary copolymer formed bycopolymerizing an olefin monomer having 2 to 8 carbon atoms, anunsaturated carboxylic acid having 2 to 18 carbon atoms and anunsaturated carboxylic acid ester with a hydroxyl group-containingcompound or an isocyanate group-containing compound; and neutralizingthe carboxylic group of said telechelic copolymer or the resultantreaction product with an inorganic metal compound.

The reaction of the telechelic copolymer with the hydroxylgroup-containing compound or the isocyanate group-containing compoundcan be suitably selected depending on functional groups introduced intothe terminals of the telechelic copolymer. For example, in the case thata functional group introduced into the terminals of the telecheliccopolymer is a carboxyl group, typically exemplified is a dehydrationcondensation reaction of the carboxyl group in said telechelic copolymerand the hydroxyl group in the hydroxyl group-containing compound. Inaddition, an embodiment where a carboxyl group other than the terminalof the telechelic copolymer is reacted with a hydroxyl group of thehydroxyl group-containing compound is also included in the presentinvention. The dehydration condensation reaction, for example, can beconducted by heat refluxing in the presence of a concentrated sulfuricacid.

Also, in the case that a functional group introduced into the terminalsof the telechelic copolymer is an isocyanate group, it is possible toselectively react the terminal isocyanate group with a hydroxyl group ofthe hydroxyl group-containing compound. Also, in the case that ahydroxyl group is introduced in the terminals of the telecheliccopolymer, the isocyanate group-containing compound is suitably reactedthereto, instead of the hydroxyl group-containing compound, or inaddition to the hydroxyl group-containing compound.

The method of ionomerization by neutralizing a carboxyl group include,for example, an embodiment where the carboxyl group of the telecheliccopolymer is neutralized beforehand, then the telechelic copolymer isreacted with the hydroxyl group-containing compound or the isocyanategroup-containing compound, or an embodiment where the carboxyl group ofthe reaction product is neutralized after the reaction product isobtained by reacting the telechelic copolymer with the hydroxylgroup-containing compound or the isocyanate group-containing compound.In a preferable embodiment, the carboxyl group of the telecheliccopolymer is neutralized beforehand, and then the telechelic copolymeris reacted with the hydroxyl group-containing compound or the isocyanategroup-containing compound.

The neutralization of the carboxyl group in the telechelic copolymer orthe resultant reaction product can be conducted, for example, in amanner where the copolymer is melted, and then a pre-determined amountof the inorganic metal compound is added to the melted copolymer, andkneaded. Specifically, the neutralization can be conducted bymelt-mixing the copolymer with an inorganic metal compound at 150 to300° C. using an extruder. Examples of the inorganic metal compound usedinclude a hydroxide, an oxide, a carbonate (carbonate salt), a hydrogencarbonate (hydrogen carbonate salt), a phosphate (phosphoric acid salt),a sulfate (sulfuric acid salt), and an acetic acid salt of the mealdescribed above, preferably the hydroxide and the oxide thereof.

(2) Golf Ball of the Present Invention

A golf ball of the present invention is not particularly limited as longas it uses the above ionomer composition for the golf ball as theconstituent composition of the golf ball. Specific examples of the golfball of the present invention are as follows.

(A) A one-piece golf ball, wherein the ionomer composition for the golfball is used as a resin component constituting a golf ball body;

(B) A two-piece golf ball comprising a core and a cover covering saidcore, wherein the above ionomer composition for the golf ball is used asa resin component constituting said core and/or the cover, morepreferably the ionomer composition for the golf ball is used as theresin component constituting the cover;

(C) A three-piece golf ball comprising a core, an intermediate layercovering said core, and a cover covering said intermediate layer,wherein the ionomer composition for the golf ball is used as a resincomponent constituting at least one of the core, the intermediate layerand the cover, and, more preferably, the ionomer composition for thegolf ball is used as the resin component constituting an outermost coverlayer;

(D) A multi-piece golf ball having at least four layers, wherein theionomer composition for the golf ball is used as a resin componentconstituting at least one of the layers; more preferably, the ionomercomposition for the golf ball is used as the resin componentconstituting an outermost cover layer; and

(E) A wound-core golf ball comprising a wound core and a cover coveringsaid wound core, wherein the ionomer composition for the golf ball isused as a resin component constituting said cover; more preferably theionomer composition for the golf ball is used as the resin componentconstituting an outermost cover layer.

The ionomer composition for the golf ball of the present invention willbe explained below in an embodiment where the ionomer composition isused as a resin component constituting a cover or an intermediate layer,but the present invention is not to be limited to the embodiment. In thecase where the cover or the intermediate layer is formed using theionomer composition for the golf ball of the present invention, as thecomposition for forming the cover or the intermediate layer(hereinafter, referred to simply as “cover (intermediate layer)composition” in some instances), the composition containing the aboveionomer composition as a resin component may be suitably used. Thecontent of the ionomer composition in the resin component of said cover(intermediate layer) composition is preferably 50 parts by mass or more,more preferably 60 parts by mass or more and even more preferably 70parts by mass or more based on the 100 parts by mass of the resincomponent. Also, as the resin component of the cover (intermediatelayer) composition, using the ionomer composition alone is also apreferable embodiment.

Furthermore, as the resin component of the cover (intermediate layer)composition, other resin component can be used together with the ionomercomposition, unless the effect of the present invention is notdeteriorated. Examples of the other resin component, in addition to theconventionally known ionomers, include a thermoplastic polyamideelastomer commercially available under a trade name “PEBAX (e.g. PEBAX2533)” from Arkema Inc., a thermoplastic polyester elastomercommercially available under a trade name “HYTREL (e.g. HYTREL 3548,HYTREL 4047)” from Du Pont-Toray Co. Ltd, a thermoplastic polyurethaneelastomer commercially available under a trade name “ERASTOLLAN (e.g.ERASTOLLAN XNY97A)” from BASF POLYURETHANE ELASTOMERS Co., and athermoplastic polystyrene elastomer commercially available under a tradename “RABALON” from Mitsubishi Chemical Corporation. Examples of theionomer resin include, in particular, an ionomer resin wherein at leasta part of carboxyl groups in a copolymer of ethylene withα,β-unsaturated carboxylic acid having 3 to 8 carbon atoms isneutralized with a metal ion; a part of carboxyl groups in a ternarycopolymer formed by copolymerizing ethylene, α,β-unsaturated carboxylicacid having 3 to 8 carbon atoms and α,β-unsaturated carboxylate isneutralized with a metal ion, or a mixture thereof.

Specific examples of the ionomer resin as exemplified in a trade nameinclude, Himilan 1555 (Na), Himilan 1557 (Zn), Himilan 1605 (Na),Himilan 1706 (Zn), Himilan 1707 (Na) and Himilan AM7311 (Mg)commercially available from Du Pont-Mitsui Polychemicals Co. Ltd.; andHimilan 1856 (Na) and Himilan 1855 (Zn) as a ternary copolymer ionomerresin.

Further, examples of an ionomer resin commercially available from DuPont Corp. include Surlyn 8945 (Na), Surlyn 9945 (Zn), Syrlyn 8140 (Na),Surlyn 8150 (Na), Surlyn 9120 (Zn), Surlyn 9150 (Zn), Surlyn 6910 (Mg),Surlyn 6120 (Mg), Surlyn 7930 (Li), Surlyn 7940 (Li) and Surlyn AD8546(Li), and examples of a ternary copolymer ionomer resin include Surlyn8120 (Na), Surlyn 8320 (Na), Surlyn 9320 (Zn) and Surlyn 6320 (Mg).

Also, examples of an ionomer resin commercially available from ExxonMobil Chemical Co. include Iotek 8000 (Na), Iotek 8030 (Na), Iotek 7010(Zn) and Iotek 7030 (Zn), and examples of a ternary copolymer ionomerresin include Iotek 7510 (Zn) and Iotek 7520 (Zn).

Additionally, Na, Zn, K, Li and Mg described in parentheses after thetrade name of the above ionomer resin indicate the kind of metal of theneutralizing metal ions. The cover (intermediate layer) composition forthe golf ball of the present invention may contain, in addition to saidionomer composition for the golf ball, a pigment component such astitanium oxide and blue pigment, a specific gravity adjusting agent suchas a calcium carbonate and a barium sulfate, a dispersing agent, anantioxidant, an ultraviolet absorbent, a light stabilizer, a fluorescentmaterial or a fluorescent brightener, to the extent that the desiredperformance is not damaged.

Also, the thickness of the cover and the intermediate layer using theionomer composition for the golf ball of the present invention ispreferably 0.1 mm or more, more preferably 0.3 mm or more, even morepreferably 0.5 mm or more, and preferably 2.0 mm or less, morepreferably 1.5 mm or less and even more preferably 1.2 mm or less. Inthe case that the thickness is less than 0.1 mm, it may be difficult tomold the cover and the intermediate layer in some instances. In the casethat the thickness is more than 2.0 mm, the cover and the intermediatelayer become too thick, and thus the resilience of the resultant golfball may decrease in some instances.

As the method for forming the cover or the intermediate layer, forexample, the cover or the intermediate layer is molded by covering acore with the cover (intermediate layer) composition. The method formolding the cover or the intermediate layer is not particularly limited,and includes, for example, a method including previously molding thecover (intermediate layer) composition into hemispherical half shells,covering the core with two half shells, and subjecting the core with thetwo half shells to the pressure molding at the temperature of 130 to170° C. for 1 to 5 minutes, or a method including injection molding thecover (intermediate layer) composition directly onto the core directlyto cover the core.

Also, in preparing the golf ball body by molding the cover, a concavitycalled dimple is generally formed on the surface. After the formation ofa cover, paint finish, stamp and the like may be carried out asrequired. Further, if necessary, the surface of the golf ball body maybe subjected to a grinding treatment like sand blast treatment toenhance the adhesion to a mark or paint film.

The above described embodiments are the case that said ionomercomposition is used as the intermediate layer or the cover in a golfball having a multi-layer structure such as two-piece golf ball,three-piece golf ball and multi-piece golf ball. In the presentinvention, said ionomer composition may be used as the core of the golfball having a multi-layer structure or the one piece golf ball body.Generally, as the core of golf ball having a multi-layer structure, aconventional rubber composition for the core can be used. The method ofmolding said ionomer composition into the core or the golf ball body isnot particularly limited, and the injection molding method of theionomer composition may be employed.

As a conventional rubber composition for the core that can be used asthe core of the golf ball having a multilayer structure, for example,without limitation, is preferably a molded body (a rubber core) which isformed by heat-pressing a rubber composition. The rubber compositionpreferably comprises a base rubber, a co-crosslinking agent, acrosslinking initiator and a filler.

As the above base rubber, a natural rubber and/or a synthetic rubber,for example, a polybutadiene rubber, a natural rubber, a polyisoprenerubber, a styrene-polybutadiene rubber and an ethylene-propylene-dienerubber (EPDM) may be used. Among them, a butadiene rubber, particularlya high cis-polybutadiene, having a cis bond of 40% or more, morepreferably 70% or more, even more preferably 90% or more is preferablein view of its superior repulsion property.

As the above crosslinking initiator, an organic peroxide may bepreferably used. Examples of the organic peroxide include dicumylperoxide, 1,1-bis (t-butylperoxy)-3,5-trimethylcyclohexane,2,5-dimethy-2,5-di (t-butylperoxy)hexane and di-t-butyl peroxide. Amongthem, dicumyl peroxide is preferably used. The amount of the organicperoxide to be blended is preferably 0.3 parts by mass or more, morepreferably 0.4 parts by mass or more, and preferably 5 parts by mass orless, more preferably 3 parts by mass or less relative to 100 parts bymass of the base rubber. If the amount is less than 0.3 parts by mass,the core becomes too soft, which tends to decrease resilience, while ifthe amount is more than 5 parts by mass, it becomes too hard, whichlowers the shot feeling.

As the above co-crosslinking agent, α,β-unsaturated carboxylic acidhaving 3 to 8 carbon atoms or the metal salt thereof may be used.Examples of the metal constituting the metal salt include zinc,magnesium, calcium, aluminum and sodium, and zinc is preferably usedpointing view of increasing resilience. Examples of the preferableα,β-unsaturated carboxylic acid and the metal salt are acrylic acid,methacrylic acid, zinc acrylate and zinc methacrylate.

The amount of the co-crosslinking agent used is 10 parts by mass ormore, more preferably 15 parts by mass or more, even more preferably 20parts by mass or more, and 55 parts by mass or less, more preferably 50parts by mass or less and even more preferably 48 parts by mass or lessrelative to 100 parts by mass of the base rubber. When the amount of theco-crosslinking agent used is less than 10 parts by mass, the amount ofthe organic peroxide used must be increased to provide a suitablehardness, which tends to decrease the resilience. On the other hand,when the amount of the co-crosslinking agent used is more than 55 partsby mass, a core becomes too hard, which may lower the shot feeling.

The above filler may be one conventionally formulated in the core of thegolf ball. The filler may include an inorganic salt, specifically, suchas a zinc oxide, a barium sulfate and a calcium carbonate, and a highspecific gravity metal powder such as a tungsten powder, a molybdenumpowder and the mixture thereof. The amount of the filler to be blendedis 0.5 parts by mass or more, preferably 1 part by mass or more, and 30parts by mass or less, preferably 20 parts by mass or less relative tothe base rubber of 100 parts by mass. If the amount is less than 0.5parts by mass, the adjustment of the specific gravity becomes toodifficult to obtain an appropriate weight, while if the amount is morethan 30 parts by mass, the resilience is lowered because of a smallrubber portion occupied in the entire core.

The above rubber composition for the core, may further contain anorganic sulfur compound, an antioxidant, or a peptizing agent, inaddition to the base rubber, the co-crosslinking agent, the organicperoxide, and the filler.

Examples of the organic sulfur compound are diphenyl disulfide;mono-substituted diphenyl disulfide such asbis(4-chlorophenyl)disulfide, bis(3-chlorophenyl)disulfide,bis(4-bromophenyl)disulfide, bis(3-bromophenyl)disulfide,bis(4-fluorophenyl)disulfide, bis(4-iodophenyl)disulfide, andbis(4-cyanophenyl)disulfide; di-substituted diphenyl disulfide such asbis(2,5-dichlorophenyl)disulfide, bis(3,5-dichlorophenyl)disulfide,bis(2,6-dichlorophenyl)disulfide, bis(2,5-dibromophenyl)disulfide,bis(3,5-dibromophenyl) disulfide, bis(2-chloro-5-bromophenyl)disulfide,and bis(2-cyano-5-bromophenyl)disulfide; tri-substituted diphenyldisulfides such as bis(2,4,6-trichlorophenyl)disulfide andbis(2-cyano-4-chloro-6-bromophenyl)disulfide; tetra-substituted diphenyldisulfide such as bis(2,3,5,6-tetrachlorophenyl)disulfide; andpenta-substituted diphenyl disulfide such asbis(2,3,4,5,6-pentachlorophenyl)disulfide andbis(2,3,4,5,6-pentabromophenyl)disulfide. These diphenyl disulfidederivatives have some sort of effect on the crosslinking state of thevulcanized rubber and thus enhance the resilience. Among them, diphenyldisulfide and bis(pentabromophenyl)disulfide are particularlypreferable, because the golf ball having the very high resilience isobtained.

The amount of the antioxidant added is preferably 0.1 parts by mass ormore, and 1 part by mass or less relative to 100 parts by mass of thebase rubber. Also, the amount of the peptizing agent is preferably 0.1parts by mass or more, and 5 parts by mass or less relative to the baserubber of 100 parts by mass.

The core is formed by kneading the above rubber composition andpress-molding it into the spherical body in the mold. The conditions forthe press-molding should be determined depending on the rubbercomposition. The press-molding is preferably carried out for 10 to 40minutes at the temperature of 130 to 180° C. under the pressure of 2.9MPa to 11.8 MPa.

The core preferably has a diameter of 30 mm or more, more preferably 32mm or more, and preferably has a diameter of 41 mm or less, morepreferably 40.5 mm or less. If the diameter of the core is less than 30mm, the thickness of the intermediate layer and the cover becomesthicker than the desired thickness and thus the resilience may belowered. On the other hand, if the diameter of the core is larger than41 mm, the thickness of the intermediate layer and the cover becomesthinner than the desired thickness and thus the intermediate layer orthe cover may not function well.

In the case that the core has a diameter of 30 mm to 41 mm, the corepreferably has a compression deformation amount (an amount shrinks alongthe direction of the compression) of 2.5 mm or more, more preferably 3.0mm or more and preferably has a compression deformation amount of 5.0 mmor less, more preferably 4.5 mm or less when applying a load from 98 Nas an initial load to 1275 N as a final load. If the compressiondeformation amount is less than 2.5 mm, the shot feeling may become baddue to the hardness, while if the compression deformation amount islarger than 5.0 mm, the resilience may become low.

The golf ball of the present invention, when it has a diameter of 42.60mm to 42.90 mm and when applying a load from an initial load of 98N to afinal load of 1275N, has an amount of compression deformation (amount ofgolf ball compressed in the direction of compression) of 2.0 mm or more,more preferably 2.1 mm or more, even more preferably 2.2 mm or more, and4.5 mm or less, more preferably 4.0 mm or less, further preferably 3.5mm or less. When the amount of compression deformation is less than 2.0mm, the shot feeling becomes hard and bad, while when the amount exceeds4.5 mm, there are some instances that resilience is lowered.

EXAMPLES

The following examples illustrate the present invention, however theseexamples are intended to illustrate the invention and are not to beconstrued to limit the scope of the present invention. Many variationsand modifications of such examples will exist without departing from thescope of the inventions. Such variations and modifications are intendedto be within the scope of the invention.

[Evaluation Methods]

(1) Slab Hardness (Shore D Hardness)

The ionomer composition and the cover (intermediate layer) compositionwere each formed into sheets each having a thickness of about 2 mm byhot press molding and the resulting sheets were maintained at 23° C. fortwo weeks. Three or more of the sheets were stacked on one another toavoid being affected by the measuring substrate on which the sheets wereplaced, and the stack was subjected to the measurement using P1 typeauto hardness tester provided with the Shore D type spring hardnesstester prescribed by ASTM-D2240, available from KOUBUNSHI KEIKI CO.,LTD.

(2) Abrasion-Resistance

A commercially available pitching wedge was attached to a swing robotavailable from Golf laboratory Co., and two points of a ballrespectively were hit once at the head speed of 36 m/sec. to observe theareas which were hit. Abrasion-resistance was evaluated and ranked intothree levels based on following criteria.

[Evaluation Criteria]

-   G(Good): Slight scratches were present on the surface of the golf    ball, but almost no care.-   F(Fair): Scratches were clearly left on the surface of the golf    ball, and a little scuffing could be observed.-   P(Poor): The surface of the golf ball was abraded considerably, and    scuffing was conspicuous.    (3) Amount of Compression Deformation (mm)

An amount of deformation in the compression direction (amount of golfball compressed in the direction of compression) was measured in each ofgolf balls or cores when applying from an initial load of 98N to a finalload of 1275N.

(4) Repulsion Coefficient of Golf Ball

Aluminum cylinder having a weight of 200 g was collided with theresultant golf ball at the speed of 45 m/sec. to measure the speed ofthe cylinder and the golf ball before and after the collision. Therepulsion coefficient of each golf ball was obtained based on each ofthe measured speed and weight. Each golf ball was measured 5 times toobtain the average. The repulsion coefficient measured in terms of eachgolf ball is reduced to an index number relative to the measured valueobtained in Golf ball No. 10 whose repulsion coefficient is assumed 100.The higher value of repulsion index indicates higher resilience.(5) Shot Feeling

The hitting test using a metal head driver W#1 was conducted by 10golfers (two professionals, eight advanced amateurs having a handicap of5 or less). Resilient feel of the impact when hitting the golf ball wasevaluated in the following criteria, and the result largest in numberwas defined as the shot feeling of the golf ball.

-   G(good): Good resilient feel-   F(fair): Average-   P(poor): Heavy feel and weak resilient feel    [Synthesis of Ionomer Composition]-   (1) To a stirring autoclave type continuous reactor of 1.5 liters in    internal volume were loaded a monomer mixture of ethylene and    methacrylic acid (ethylene: methacrylic acid=80:10 by mass) and    2,2′-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate (V-057    available from Wako Pure Chemical Ltd.) as a radical polymerization    initiator of 4 ppm by mass relative to the monomer mixture, and the    reaction was carried out at 160° C. while keeping a pressure in the    reactor at 1600 kg/cm². The resultant copolymer and unreacted    monomer were discharged into a separation container through an    adjusting valve, followed by separation of the copolymer to give a    copolymer in which carboxyl groups were introduced at both    terminals. The resultant ethylene-methacrylic acid copolymer having    both terminated carboxyl group of 90 parts by mass and    1,4-butanediol of 10 parts by mass were dissolved in toluene, and    concentrated sulfuric acid was added thereto as a catalyst, and    heated to reflux to conduct the dehydration condensation reaction    between the ethylene-methacrylic acid copolymer having both    terminated carboxyl group and 1,4-butadiol. Then toluene was    distilled out with an evaporator, and sodium hydroxide was blended    so as to neutralize 50 mole % of the carboxyl group in the resultant    reaction product, and extruded by a twin-screw kneading extruder to    give the ionomer composition 1.-   (2) The ionomer composition 2 was produced in the same manner as in    the ionomer composition 1 except that zinc hydroxide was used to    neutralize 70 mole % of carboxyl group in the resultant reaction    product instead of sodium hydroxide.-   (3) The ionomer composition 3 was produced in the same manner as in    the ionomer composition 1 except that a monomer mixture of ethylene    and methacrylic acid (ethylene: methacrylic acid=70:10 by mass) was    used as a monomer mixture, and that using the resultant    ethylene-methacrylic acid copolymer of 80 parts by mass and    polyoxytetramethylene glycol (molecular weight of 1000) of 20 parts    by mass as the hydroxyl group-containing compound to carry out the    dehydration condensation reaction.-   (4) The ionomer composition 4 was produced in the same manner as in    the ionomer composition 3 except that zinc hydroxide was used to    neutralize 70 mole % of carboxyl group in the resultant reaction    product instead of sodium hydroxide.-   (5) The ionomer composition 5 was produced in the same manner as in    the ionomer composition 1 except that a monomer mixture of ethylene    and methacrylic acid (ethylene: methacrylic acid=66:9 by mass) was    used as a monomer mixture, and that using the resultant    ethylene-methacrylic acid copolymer of 75 parts by mass and    polyoxytetramethylene glycol (molecular weight of 3000) of 25 parts    by mass as a hydroxyl group-containing compound to carry out the    dehydration condensation reaction.-   (6) The ionomer composition 6 was produced in the same manner as in    the ionomer composition 5 except that zinc hydroxide was used to    neutralize 70 mole % of carboxyl group in the resultant reaction    product instead of sodium hydroxide.-   (7) To a stirring autoclave type continuous reactor of 1.5 liters in    internal volume were loaded a monomer mixture of ethylene and    methacrylic acid (ethylene: methacrylic acid=80:10 by mass) and    2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] (VA-086    manufactured by Wako Pure Chemical Ltd.) as a radical polymerization    initiator of 4 ppm by mass relative to the monomer mixture, and    reaction was carried out at 160° C. while keeping a pressure in the    reactor at 1600 kg/cm². The resultant copolymer and unreacted    monomer were discharged into a separation container through an    adjusting valve, followed by separating the copolymer to give a    copolymer in which hydroxyl groups were introduced in both terminals    (weight average molecular weight of 80000, OH value of 5 mg KOH/g).    Sodium hydroxide was blended to neutralize 50 mole % of the carboxyl    group of the copolymer, extruded using a twin-screw kneading    extruder at 140° C. to give the telechelic copolymer ionomer. The    telechelic copolymer ionomer and 4,4′-diphenylmethane    diisocyanate (MDI) as a polyisocyanate were blended so that NCO/OH    (mole ratio)=1.1, reacted in toluene at 60° C., then toluene was    distilled out with an evaporator to give an ethylene-methacrylic    acid copolymer ionomer having isocyanate groups introduced in both    terminals (content of isocyanate group of 0.4%). Sequentially, the    resultant ethylene methacrylic acid copolymer ionomer having    terminal isocyanate groups and polyoxytetramethlene glycol    (molecular weight of 1000) as the hydroxyl group-containing compound    were reacted so that NCO/OH (mole ratio)=1.0 to give ionomer    composition 7.-   (8) Ionomer composition 8 was produced in the same manner as in the    ionomer composition 7 except that zinc hydroxide was used to    neutralize 70 mole % of the carboxyl group, instead of sodium    hydroxide.    [Production of the Golf Ball]    (1) Production of the Core

The rubber composition shown in Table 1 was kneaded, and pressed inupper and lower molds each having a spherical cavity at the heatingcondition of 170° C. for 20 minutes to obtain the solid core in aspherical shape.

TABLE 1 Core composition A B Polybutadiene rubber 100 100 Zinc acrylate29 28 Zinc oxide 5 5 Barium sulfate appropriate amount appropriateamount* Pentabromo disulfide 0.5 0.5 Dicumyl peroxide 0.9 0.7 Corediameter (mm) 39.5 37.4 Compression 3.2 3.5 deformation amount of core(mm) Formulation: parts *Adjustment for a golf ball to weigh 45.4 gaccording to the composition of cover Notes on Table 1 Polybutadienerubber: BR-18 (high-cis polybutadiene) available from JSR CorporationZinc acrylate: ZNDA-90S available from Nihon Jyoryu Co. Ltd. Zinc oxide:Ginrei R available from Toho Zinc Co. Ltd. Barium sulfate: Bariumsulfate BD available from Sakai Chemical Industry Co. Ltd. Dicumylperoxide: Percumyl D available from NOF Corporation The amount of bariumsulfate was appropriately adjusted to obtain the golf ball having a massof 45.4 g.(2) Preparation of the Cover (Intermediate Layer) Composition

The materials shown in Table 2 were mixed using a twin-screw kneadingextruder to obtain the cover (intermediate layer) composition in theform of pellet as shown in Table 3. The extrusion was conducted in thefollowing conditions:

screw diameter=45 mm,

screw revolutions=200 rpm,

screw L/D=35, and

the cover (intermediate layer) composition was heated to from 160° C. to230° C. at the die position of the extruder.

TABLE 2 Degree of Neutralizing neutralization Shore D CompositionMonomer composition (mass ratio) metal (mol %) hardness Ionomercomposition 1 Ethylene (80) Methacrylic acid (10) 1,4-butanediol (10) Na50 54 Ionomer composition 2 Ethylene (80) Methacrylic acid (10)1,4-butanediol (10) Zn 70 54 Ionomer composition 3 Ethylene (70)Methacrylic acid (10) PTMG-1000 (20) Na 50 45 Ionomer composition 4Ethylene (70) Methacrylic acid (10) PTMG-1000 (20) Zn 70 45 Ionomercomposition 5 Ethylene (66) Methacrylic acid (9) PTMG-3000 (25) Na 50 34Ionomer composition 6 Ethylene (66) Methacrylic acid (9) PTMG-3000 (25)Zn 70 34 Ionomer composition 7 Ethylene (70) Methacrylic acid (10)PTMG-1000 Na 50 44 Ionomer composition 8 Ethylene (70) Methacrylic acid(10) PTMG-1000 Zn 70 44 Himilan 1605 Ethylene Methacrylic acid — Na — 65Himilan AM7329 Ethylene Methacrylic acid — Zn — 65 Himilan 1856 EthyleneMethacrylic acid Acrylic acid ester Na — 52 Himilan 1855 EthyleneMethacrylic acid Acrylic acid ester Zn — 54 Surlyn 8320 EthyleneMethacrylic acid Acrylic acid ester Na — 36 Himilan AM7316 EthyleneMethacrylic acid Acrylic acid ester Zn — 34 ELASTOLLAN XNY97AThermoplastic urethane — 48

TABLE 3 Cover (intermediate layer) composition 1 2 3 4 5 6 7 8 9 10 1112 13 14 Materials Ionomer composition 1 50 — — — — — 50 — — — — — — —Ionomer composition 2 50 — — — — 50 — — — — — — — Ionomer composition 3— 50 80 20 — — — — — — — — — — Ionomer composition 4 — 50 20 80 — — — —— — — — — — Ionomer composition 5 — — — — 50 — — — — — — — — — Ionomercomposition 6 — — — — 50 — — — — — — — — — Ionomer composition 7 — — — —— — — — — — — — — 50 Ionomer composition 8 — — — — — — — — — — — — — 50Himilan 1605 — — — — — 50 — — — — 50 — 50 — Himilan AM7329 — — — — — —50 — — — — — 50 — Himilan 1856 — — — — — — — 50 — — — — — — Himilan 1855— — — — — — — 50 60 — 50 — — — Surlyn 8320 — — — — — — — — 40 50 — — — —Himilan AM7316 — — — — — — — — — 50 — — — — ELASTOLLAN XNY97A — — — — —— — — — — — 100  — — Titanium oxide  2  2  2  2  2  2  2  2  2  2  2  2 2  2 Slab hardness (Shore D) 57 48 47 46 36 62 61 56 48 36 62 48 66 46Notes on Table 3

Himilan: an ionomer resin manufactured by Du Pont-Mitsui PolychemicalsCo. Ltd.

Surlyn: an ionomer resin manufactured by Du Pont Corporation

Erastollan XNY97A: a thermoplastic urethane elastomer manufactured byBASF Japan Ltd.

(3) Production of the Golf Ball Body

The cover (intermediate layer) composition obtained as described abovewas injection molded onto the core obtained as described above to formthe intermediate layer covering said core and/or the cover. The upperand lower molds for forming the cover have a spherical cavity havingdimples. The part of the dimples can serve as a hold pin which isretractable. When forming the golf ball body, the hold pins wereprotruded to hold the core, and the resin heated at 210° C. was chargedinto the mold held under the pressure of 80 tons for 0.3 second. Afterthe cooling for 30 seconds, the molds were opened and then the golf ballbody was discharged. The surface of the resultant golf ball wassubjected to a sand blast treatment, and marking, and then applied witha clear paint thereto, the paint was dried in an oven at 40° C. to givea golf ball having a diameter of 42.7 mm and a mass of 45.4 g.

The evaluation results of the golf balls obtained are shown in Table 4regarding the composition of golf ball, abrasion-resistance, flightdistance, shot feeling and amount of spin.

TABLE 4 Golf ball No. No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No. 7 No. 8No. 9 No. 10 No. 11 No. 12 No. 13 No. 14 No. 15 Type of core A B A A A AA A A A A A A A A Intermediate layer — 13 — — — — — — — — — — — — —composition Thickness of inermediate — 1.5 — — — — — — — — — — — — —layer (mm) Cover composition 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14Thickness of cover (mm) 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.21.2 1.2 1.2 Compression deformation 2.9 2.7 3.0 3.0 3.0 3.1 2.7 2.7 2.93.0 3.1 2.7 3.1 2.5 3 amount of core (mm) Resilience index 102 103 101101 101 100 103 103 101 100 99 101 98 103 101 Shot feeling G G G G G G GG F F F G F F G Abrasion-resistance G G G G G G G G P P P F G F G

In Table 4, golf balls of No. 1 to No. 8, and No. 15 are the case thatthe cover was produced using the ionomer composition comprising areaction product obtained by reacting the telechelic copolymer having afunctional group introduced into both terminals of the binary copolymerformed by copolymerizing the olefin monomer having 2 to 8 carbon atomsand the unsaturated carboxylic acid having 2 to 18 carbon atoms with thehydroxyl group-containing compound, wherein at least 10% of thecarboxylic group in said reaction product is neutralized with aninorganic metal. All of the golf balls were excellent in balance offlight distance (resilience), abrasion-resistance and shot feeling. Golfballs No. 9 to No. 12 and No. 14 are the case that mixtures of theconventional ionomer resins were used. All of them had poorabrasion-resistance, and the shot feeling was bad in golf balls No. 9 toNo. 11. Also, in golf ball No. 13 an urethane cover was used, where thecoefficient of resilience and shot feeling were both lowered.

The present invention can provide a golf ball having well-balancedflight distance (resilience), abrasion-resistance and shot feeling. Theionomer composition of the present invention is preferable particularlyfor a golf ball cover.

This application is based on Japanese Patent application No. 2006-002923filed on Jan. 10, 2006, the contents of which are hereby incorporated byreference.

1. An ionomer composition for a golf ball comprising a reaction productobtained by reacting a telechelic copolymer having functional groupsintroduced in both terminals of a binary copolymer formed bycopolymerizing an olefin monomer having 2 to 8 carbon atoms and anunsaturated carboxylic acid having 2 to 18 carbon atoms, and/or aternary copolymer formed by copolymerizing an olefin monomer having 2 to8 carbon atoms, an unsaturated carboxylic acid having 2 to 18 carbonatoms and an unsaturated carboxylic acid ester with a hydroxylgroup-containing compound or an isocyanate group-containing compound,wherein at least 10 mole % of a carboxylic group in said reactionproduct is neutralized with an inorganic metal.
 2. The ionomercomposition for the golf ball according to claim 1, wherein the terminalgroup of said telechelic copolymer is at least one member selected fromthe group consisting of a carboxylic group, a hydroxyl group, an aminogroup, an isocyanate group, halogen, a nitro group, a thiol group and anepoxy group.
 3. The ionomer composition for the golf ball according toclaim 1, wherein said hydroxyl group-containing compound is a polyolhaving a molecular weight of 200 to
 10000. 4. The ionomer compositionfor the golf ball according to claim 3, wherein said hydroxylgroup-containing compound is polyoxytetramethylene glycol (PTMG) havinga molecular weight of 1000 to
 3000. 5. The ionomer composition for thegolf ball according to claim 1, wherein the reaction product is obtainedby a dehydration condensation reaction between the carboxyl group ofsaid telechelic copolymer and the hydroxyl group of the hydroxylgroup-containing compound.
 6. The ionomer composition for the golf ballaccording to claim 1, wherein the telechelic copolymer is the binarycopolymer of ethylene and methacrylic acid, or the ternary copolymer ofethylene, methacrylic acid, and an acrylic acid ester.
 7. The ionomercomposition for the golf ball according to claim 1, content of theolefin monomer in the binary or ternary copolymer is from 50% to 80% bymass.
 8. The ionomer composition for the golf ball according to claim 1,content of the unsaturated carboxylic acid in the ternary copolymer isfrom 8% to 30% by mass.
 9. The ionomer composition for the golf ballaccording to claim 1, wherein a degree of neutralization of thecarboxylic group in the reaction product is from 30 mole % to 80 mole %.10. The ionomer composition for the golf ball according to claim 1,wherein the inorganic metal is an alkali metal.
 11. A production methodof an ionomer composition for a golf ball, comprising the steps of:obtaining a reaction product by reacting a telechelic copolymer havingfunctional groups introduced in both terminals of a binary copolymerformed by copolymerizing an olefin monomer having 2 to 8 carbon atomsand an unsaturated carboxylic acid having 2 to 18 carbon atoms, and/or aternary copolymer formed by copolymerizing an olefin monomer having 2 to8 carbon atoms, an unsaturated carboxylic acid having 2 to 18 carbonatoms and an unsaturated carboxylic acid ester with a hydroxylgroup-containing compound or an isocyanate group-containing compound;and neutralizing the carboxylic group of said telechelic copolymer orthe resultant reaction product with an inorganic metal compound.
 12. Theproduction method of the ionomer composition for the golf ball accordingto claim 11, carrying out a dehydration condensation reaction betweenthe carboxylic group of said telechelic copolymer and the hydroxyl groupof the hydroxyl group-containing compound.
 13. The production method ofthe ionomer composition for the golf ball according to claim 11, whereinan isocyanate group is introduced as the terminal functional group ofsaid telechelic copolymer, and the terminal isocyanate group of saidtelechelic copolymer is reacted with the hydroxyl group of said hydroxylgroup-containing compound.
 14. The production method of the ionomercomposition for the golf ball according to claim 11, wherein thetelechelic copolymer is neutralized beforehand, then the telecheliccopolymer is reacted with the hydroxyl group-containing compound or theisocyanate group-containing compound.
 15. The production method of theionomer composition for the golf ball according to claim 11, wherein thecarboxyl group of the reaction product is neutralized after the reactionproduct is obtained by reacting the telechelic copolymer with thehydroxyl group-containing compound or the isocyanate group-containingcompound.
 16. A one-piece golf ball, wherein the ionomer composition forthe golf ball of claim 1 is used as a resin component constituting agolf ball body.
 17. A two-piece golf ball comprising a core, and a covercovering said core, wherein the ionomer composition for the golf ball ofclaim 1 is used as a resin component constituting said core and/or thecover.
 18. A three-piece golf ball comprising a core, an intermediatelayer covering said core, and a cover covering said intermediate layer,wherein the ionomer composition for the golf ball of claim 1 is used asa resin component constituting at least one of the core, theintermediate layer and the cover.
 19. A multi-piece golf ball having atleast four layers, wherein the ionomer composition for the golf ball ofclaim 1 is used as a resin component constituting at least one layerthereof.